1. Field of the Invention
This invention relates to a driving power transmitting system of a vehicle.
2. Description of the Related Art
Conventionally, there has been known a power transmitting system in which driving power is transmitted from an input shaft of the system to an output shaft for front wheels and an output shaft for rear wheels as shown in Japanese Utility Model Public Disclosure No. 1-149057, laid open to the public in 1989.
The power transmitting system disclosed in this Japanese document pertains to so a called a part time 4WD system on a continuous rear wheel drive system. In the part time 4WD system, the driving power is transmitted to the output shaft for the rear wheels continuously through a switching mechanism and a differential mechanism and on and off to the output shaft for the front wheels when desired. In order to transmit the driving power to the output shaft for the front wheels at the desired operation, there is provided a drive mode switching mechanism for selectively establishing, one of three different drive modes for driving the wheel. In the first drive mode, the driving power from the differential mechanism is transmitted to only the rear wheels so that a two wheel drive mode is established. In second drive mode, the driving power in the differential mechanism is transmitted to both output shafts for the front and rear wheels to allow a speed difference between the front and rear wheels and establish a differential four wheel drive mode in which a center differential gear mechanism is unlocked to allow differential operation between the output shafts for the front and rear wheels. In third drive mode, the driving power is transmitted to both the front and rear wheels so as to prohibit differential movement a locked four wheel drive mode in which the center differential mechanism is locked.
The power transmitting mechanism disclosed in Japanese Utility
Model Public Disclosure No. 1-149057 is provided with a sleeve in the switching mechanism which is moved longitudinally so that a spline of the sleeve is selectively brought into engagement with a spline of the output shaft for the front wheels, a spline of the input shaft and a spline of the output shaft for the rear wheels.
For switching the drive mode of the vehicle, another switching mechanism is known utilizing a clutch mechanism. This type of switching mechanism is disclosed in Japanese Patent Public Disclosure No. 1-278841, laid open to the public in 1989 and is provided with a clutch mechanism which is operated to be engaged and disengaged so as to establish selectively one of the drive modes allowing differential movement between the output shafts for the front wheels and the rear wheels and prohibiting the differential movement. In order to accomplish such operation of the clutch mechanism, there is provided a electromagnet in the mechanism to be energized or disenergized.
Japanese Patent Public Disclosure No. 63-192620, laid open to the public on Aug. 10, 1988, also discloses similar type of power transmitting system.
It should, however, be noted that the conventional switching mechanism having a clutch mechanism and an electromagnet for driving the clutch mechanism makes the switching mechanism bulky.